Cyano-functionalized carbazole substituted pyrene derivatives for promising organic light-emitting diodes

Balanced charge transport is crucial to realize efficient organic light-emitting diodes. In this work, pyrene derivatives featuring variable number of cyano-functionalized carbazoles are synthesized and characterized by photophysical, electrochemical, thermal and electroluminescence studies. The compounds displayed progressive variation in absorption and emission wavelength reflecting the effect of chromophore loading. The electroluminescence color change from deep blue to green on varying the number/position of cyanocarbazole units on pyrene. 1,6-Disubstituted derivative exhibited blue shift in absorption and emission when compared to the 1,8-analog. The current efficiency and power efficiency of the devices progressively increase on increasing the cyanocarbazole load on pyrene. It is probably originating from the balanced charge transport due to the increase in the number of cyanocarbazole units on pyrene and effective harvest of excitons in emissive layer. The best electroluminescence performance of the doped device fabricated from tetra-substituted derivative (1 wt%) displayed relatively high power efficiency (5.8 lm/W) and current efficiency (9.2 cd/A).